Caption: False-colour bubble chamber photograph of the production & decay of a lambda particle. A proton (yellow) enters from the bottom & knocks out an atomic electron (green) before colliding with a proton at rest in the chamber's liquid hydrogen. The collision produces 7 negative pions (blue), 9 positive particles (red), which include a proton & a kaon as well as 7 positive pions, & the lambda - which is neutral & therefore invisible. The lambda moves upwards & betrays itself when it decays into a proton (yellow) & a negative pion (purple). Pos- itive particles curve clockwise, negative partic- les anticlockwise in the chamber's magnetic field. Taken at the 80-inch (200cm) bubble chamber at BNL on Long Island, New York.